Biol. Unit 4, Chapter 4 - Energy in Ecosystems

Ajay RaiEnergy in ecosystems:Energy transfer:Organisms that produce energy containing organic molecules, using an external energy source, tomake inorganic molecules react together are known as producers. This is usually carried out viaphotosynthesis. The entire community relies on the producers. All of the remaining organisms areknown as consumers.Organisms that feed directly on producers are primary consumers and are usually herbivores.Animals that eat primary consumers are secondary consumers. Above them are tertiaryconsumers and so on. This sequence forms a food chain. A food chain is the sequence in whichenergy is passed from one organism to another, in the form of chemical energy in organicnutrients.Each step in the food chain is known as a trophic level. Organisms that feed on dead bodies andwaste matter from all trophic levels are known as decomposers.Energy loss:Not all of the energy from the sun is used by leaves. Some solar energy is reflected, somepasses straight through the leaves, some is the wrong wavelength and some is converted intoheat during photosynthesis. Around 90% of energy is lost through trophic levels.Energy is also lost through food as some parts of it, bones & roots, are not eaten so energy isnot taken in and some parts of food are indigestible and so pass straight through the organism.Productivity:The rate at which a plant produces organic materials through photosynthesis is its gross primaryproductivity (GPP).However a lot of this energy is lost to the environment when organisms use energy producedfrom respiration for movement or body heat. This is called respiratory loss.The net gain of dry mass, or biomass, stored in the plant after respiration is known as the netprimary productivity (NPP).NPP = GPP ­ respiration or net productivity = gross productivity ­ respiratory loss.Energy in ecosystems